The child was with his mother visiting the Pittsburgh Zoo & PPG Aquarium. He fell about 11 feet off a railing that his mother had put him on top of to view the animals, police said.

He was immediately attacked by several dogs, zoo President and CEO Barbara Baker said. It is unclear whether the boy died from the fall or from being attacked by the animals.

"The screams just kept coming and coming: 'Someone help. Someone has to do something,'" Angela Cinti, 20, of Bethel Park, who was visiting the zoo with her boyfriend, told the Pittsburgh Post-Gazette.

The zoo quickly moved visitors into buildings as animal keepers tried to coax the dogs into an off-exhibit area. Many of the 11 dogs in the exhibit moved away immediately, and several others were scared away from the child by the zookeepers. A remaining dog would not leave the child, and a Pittsburgh police officer shot the animal.

Baker pointed out these types of dogs typically hunt in packs, so this behavior is not considered unusual.

No visitors on the observation deck saw the child fall into the exhibit, Baker said.

The zoo was closed for the day while police and zoo officials investigate.

Authorities didn't immediately release the name of the boy or his mother, but say she is 34 years old and lives in Pleasant Hills, just outside Pittsburgh. The boy's father arrived on the scene soon after the accident, police said.

NBC News

African painted dogs, also known as African wild dogs, Cape hunting dogs, spotted dogs, and painted wolves, are found in the open plains and sparse woodlands of sub-Saharan Africa. The long-legged canines have only four toes per foot.

According to the zoo’s website, African painted dogs are the size of medium domestic dogs, weighing on average between 37 and 80 pounds and measuring 24 to 30 inches high.

The dogs normally live in a 1.5-acre exhibit called the Painted Dog Bush Camp that's part of a larger open area called the African Savanna, where elephants, lions and other animals can be seen.

In May, some of the dogs crawled under a fence and escaped into a part of the exhibit that's usually closed. The animals were lured back in with food and no one was hurt.

Ten African painted dogs were born at the zoo in 2009, and their mother died of a ruptured uterus shortly after delivering the litter. Five of the pups survived. The mortality rate for painted pups is 50 percent, even when born in the wild to a healthy mother.

It was only the second litter to be hand-raised in captivity, along with one in the United Kingdom, zoo officials said at the time.